It is known to use refrigerants such as R12, R134a, and CO2 in an air conditioning system for a vehicle. However, environmental concerns exist with these refrigerants. As a result, legislation has been passed by various governmental agencies of the United States and the European Union, for example, requiring that the air conditioning system operate with substantially no refrigerant leaks or permeation. Even where R1234yf refrigerant is employed in the air conditioning system, leakage concerns exist due to the flammability of the refrigerant.
A thermal expansion valve (often abbreviated as TXV or TX valve) is a component in refrigeration and air conditioning systems that controls the amount of refrigerant flow into an evaporator. The thermal expansion valve thereby controls the fluid temperature at the outlet of the evaporator. This is accomplished by use of a temperature sensing bulb filled with a gas that causes the thermal expansion valve to open against the spring pressure in the valve body as the temperature of the bulb increases. As the temperature in the evaporator decreases, so does the pressure in the bulb, and therefore, the pressure on the spring, causing the thermal expansion valve to close.
The thermal expansion valve is a key element to a refrigeration or air conditioning cycle. The basic refrigeration cycle consists of four major elements: a compressor; a condenser; a metering device; and an evaporator. As the refrigerant passes through a circuit containing these four elements, air conditioning occurs. The cycle starts when the refrigerant enters the compressor in a low pressure, low temperature, and gaseous form. The refrigerant is compressed by the compressor to a high pressure and high temperature gaseous state. The high pressure and high temperature gas then enters the condenser. The condenser condenses the high pressure and high temperature gas to a high temperature liquid by transferring heat to a lower temperature media, usually ambient air. The high temperature liquid then enters the thermal expansion valve where it undergoes an adiabatic expansion, and results in a low pressure and low temperature liquid suitable for cooling. The low temperature and pressure liquid enters the evaporator where heat is transferred from the ambient air to the refrigerant, causing the refrigerant to boil and return to the low pressure, low temperature, and gaseous form. The low pressure and low temperature gas enters the compressor and the cycle repeats.
The thermal expansion valve, as well as other multi-port devices in the air conditioning system such as a condenser manifold and an in-line tube manifold, typically uses a double fitting with either rubber o-ring seals or rubber gasket seals. However, the rubber seals can leak due to permeation, mis-assembly and contamination of the sealing surface.
There is a continuing need for a multi-port device such as a thermal expansion valve for use in an air conditioning system, which minimizes a leaking of a fluid such as refrigerant from the air conditioning system.